Hypoxia is a frequent tumour characteristic associated to aggressive tumours and a reduced therapeutic response. In radiotherapy the reduced response is mainly due to hypoxia induced radio-resistance, which takes place, when there is a lack of oxygen to react with the free radicals released during irradiation thereby reducing the formation of damaging compounds inside the tumour. But hypoxia is also a clinical problem that can potentially be reduced by supplying the radiation therapy with hypoxia-modifying therapy. By adding a hypoxia-modifying agent for example a hypoxic sensitizer such as nitroimidazole to the treatment, reactive NO2-groups are supplied, that under anaerobic conditions can form damaging compounds similar to the oxygen-free radicals. Thus, by this additive action it is possible to improve the therapeutic response in the hypoxic tumours, which has also been verified in the DAHANCA 5 trial, where head and neck cancer patients treated with the hypoxic sensitizer nimorazole in conjunction with radiotherapy obtained an improved outcome compared to those treated with placebo. But not all tumours are hypoxic in a degree which justifies the use of hypoxia-modifying agents, since treatment including administration of hypoxia-modifying agents has side effects unpleasant to the diseased individual. One of the conclusions from the DAHANCA 5 trial was that there is a demand for better methods to detect tumour hypoxia, and thereby to help in the identification of those patients that will benefit from the hypoxia modifying therapy.
Well established approaches concerning the characterization of hypoxic tumour-status include the use of oxygen sensing electrodes, the infusion of exogenous hypoxic tracers (pimonidazole, 18F-miso, 18F-FAZA) or the quantification of endogenous markers related to the hypoxia-induced HIF-1α cascade (Moon et al., The potential role of intrinsic hypoxia markers as prognostic variables in cancer. Antioxid Redox Signal 9:1237-1294, 2007). These methods all contribute with important information, but are also coupled with disadvantages either in the form of mandatory invasive procedures or inadequate specificity concerning the association to hypoxia.
With cDNA microarray technology and gene expression profiling it has become possible to identify groups of genes (signatures, profiles, metagenes) characterized by being up- or down-regulated under certain relevant conditions. Also, signatures focusing on hypoxia have been developed. These signatures have increased our understanding of the microenvironment and hypoxia-regulated cell metabolism but they also carry the potential benefit of making us able to evaluate the hypoxic status of a tumour based on the expression of specific hypoxia responsive genes in the tumour biopsy. The clinical relevance of such “hypoxia gene expression signatures” has been described by more groups. In 2006, Chi et al suggested a range of 168 in vitro derived hypoxia responsive genes that also proved to be a strong predictor of clinical outcome in series of breast and ovarian cancers (Chi et al., Gene expression programs in response to hypoxia: Cell type specificity and prognostic significance in human cancers. PLoS Med 3:e47, 2006). Winter et al have developed a hypoxic signature, containing 99 genes, which proved to be an independent prognostic factor for recurrence free survival in a publically available head and neck cancer set and a significant prognostic factor for overall survival in a published breast cancer series. (Winter et al., Relation of a hypoxia metagene derived from head and neck cancer to prognosis of multiple cancers. Cancer Res 67:3441-3449, 2007). Based on in silico analysis of a core of genes from this signature, Buffa et al defined a “common hypoxia metagene” with even further prognostic impact (Buffa et al., Large meta-analysis of multiple cancers reveals a common, compact and highly prognostic hypoxia metagene. Br J Cancer 102:428-435, 2010). As stated with these studies, gene expression signatures focusing on hypoxia makes up a promising strategy concerning hypoxic classification and the prediction of outcome in more cancers.
But according to existing literature, no final hypoxic signature has yet been obtained and implemented as predictor of additive treatment with hypoxia modifying therapy in the clinical setting.
A developing strategy concerning this obstacle is to use the expression of hypoxia responsive genes in the tumour biopsy as an evaluation of the present oxygen status in the tumour and thereby to guide the treatment in according to this evaluation.
The present invention presents a method for determining the prognostic and predictive impact of the oxygen status of the tumour based on measuring the transcriptional levels of specific genes in the tumour, which are also correlated to hypoxia status.